The invention relates to a liquid, solvent-free or low-solvent hardenable polyurethane-bitumen-plasticizer-one-component composition, a process for the production thereof and the use thereof.
Bitumens are extremely complex mixtures which mainly comprise polycyclic hydrocarbons and oxygen compounds. A clear distinction must be made between the terms bitumen and asphalt and the terms tar and pitch (cf. DIN 55 946). According to the relevant literature (e.g. "Bitumen" by K. H. Gusfeldt, Deutsche Shell AG in Ullmanns Enzyklopadie der Technischen Chemie, fourth edition, Weinheim 1974, vol. 8, pp 527 to 541) bitumens are the dark-coloured, semisolid to brittle, meltable, high molecular weight hydrocarbon mixtures obtained during the careful processing of crude oils and the natural asphalt fraction soluble in carbon disulphide (CS.sub.2). A distinction is made between different bitumen types, such as distillate bitumen, blown bitumen, high vacuum bitumen and cut-back bitumen.
Within the scope of the present invention the term bitumen also covers asphalts, which are mixtures of bitumen and mineral subtances. Such asphalts are e.g. asphalt concrete, cast asphalt, asphalt mastic and natural asphalts, which are naturally occurring mixtures of bitumen and mineral substances.
As stated hereinbefore, tars and pitches are not covered by the present invention. Tars are liquid to semisolid products obtained through decomposing thermal treatment of organic natural substances (&lt;700.degree. C.: low temperature tars; 900.degree. to 1300.degree. C.: high temperature tars) which are designated as a function of the origin of the natural substance, e.g. coal tars, lignite tars, wood tars, peat tars and oil shale tars. Tars are generally dark to black viscous liquids with low proportions of emulsified water and dispersed carbon-rich solid particles entrained during formation (so-called tar sediments).
Pitches, however, are the residue of tar distillation. As a function of their origin, distinction is made between coal tar pitches, petroleum pitches, tall oil pitches, fish oil pitches, etc. Pitches are generally dark to black thermoplastic subtances with a broad molecular weight range (i.e. so-called multicomponent mixtures of higher molecular weight components).
Another way to distinguish between bitumens/asphalts and tars/pitches is provided by their toxicology. As opposed to coal tar, bitumen or asphalt contains no carcinogenic polycyclic hydrocarbons. By definition tars and pitches are produced by decomposing heat treatment at temperatures above 500.degree. C. (see above). During the pyrolysis of organic materials carcinogenic polycyclic aromatic hydrocarbons form at temperatures above 500.degree. C. At least 20 such different powerful carcinogens have already been detected in tars and pitches. The most powerful carcinogens from among the polycyclic aromatic hydrocarbons have been found in the case of compounds with 5 or more benzene rings, e.g. benzopyrene. In the case of high temperature tars (&gt;1000.degree. C.) inter alia there is also a formation of 7,12-dimethyl-benzanthracene, which animal experiments have shown to be highly carcinogenic. Tars and pitches also contain 2-naphthylamine, a well-known carcinogenic subtance (cf. e.g. "Teer und Pech", G. Collin/M. Zander, Rutgerswerke AG in Ullmanns Enzyklopadie der Technischen Chemie, fourth edition, Weinheim, 1982, vol. 22, pp 411 to 455).
Whereas tars and pitches are considered carcinogenic substances, bitumens and asphalts are non-carcinogenic. In this connection it is pointed out that the literature often does not logically adhere to the above clearly defined restriction between the terms bitumen/asphalt and tar/pitch. Thus, e.g. reference is sometimes made to bituminous materials, without clearly defining this term, because it is frequently intended to cover tars and pitches. According to the invention only bitumen (including asphalt) is to be used, whereas tars and pitches are expressly excluded.
Bitumens have in general a very good resistance to water and weather. Thus, products based on such bitumens have long been used as water and weather-resistant mastics, paints, road coverings, corrosion-preventing varnishes, coating compounds, etc.
As bitumen-containing systems in the unmodified state and in particular under varying climatic conditions, particularly under the action of heat and cold, either soften (in the case of heat) or embrittle (in the case of cold) as a result of their thermoplastic ductility (deformability), attempts have been made to modify such bitumen-containing systems so as to avoid the disadvantages linked with the ductility.
Numerous bitumen modifications have been considered and in part also used, such as e.g. modifications of
1. bitumen-mineral oil, PA1 2. bitumen-wax, PA1 3. bitumen-elastomer (e.g. NR, SBR, EPDM, etc.), and PA1 4. bitumen-polymer (e.g. PE, PP, ethylene copolymers, etc.)
The proportion of the modification component was generally well below that of the bitumen, whereas the polyurethane proportion in the inventive composition is essentially the same as the bitumen proportion, i.e. the weight ratio of the polyurethane modification component to the bitumen is preferably 50:50.
The aforementioned conventional bitumen modifications generally led to a certain improvement in the thermoplastic ductility of the bitumen fraction, but the mainly thermoplastic nature of such modified bitumen systems was largely retained.
Bitumen-polyurethane or polyurethane-bitumen modifications, particularly with liquid polyurethane prepolymers, are not known. There are several different reasons for this. One of the reasons is the known incompatibility of polyurethane prepolymers with bitumen, particularly in solvents, the discovery of suitable solvent systems for polyurethanes and bitumens being particularly problemmatical. Conventionally and preferably bitumen is soluble in gasoline hydrocarbons, such as white spirit, or in aromatic mineral oils and the like. Polyurethane prepolymers, e.g. based on polypropylene glycoldiol-diphenylmethane-4,4'-diisocyanate-polyadducts (PPG-MDI prepolymers) are, however, not soluble in such gasoline hydrocarbons and mineral oils. Other more or less polar solvents, such as chlorinated hydrocarbons, aromatic hydrocarbons, esters, ketones, etc., which might be considered as joint solvents are frequently unusable or undesirable due to solvent sensitivity with respect to materials the bitumens are used in connection with, i.e. expanded polystyrene foams, or due to health considerations in the workplace.
It was therefore not hitherto possible for the above reasons to combine (liquid) polyurethane prepolymers with (solid) bitumens in a one-component, solvent-free, storage-stable form (cf. e.g. Encyclopedia of Polymer Science and Technology, New York-London-Syndey, 1965, vol. 2 p. 423).
The aforementioned incompatibilities are accompanied by a chemically caused incompatibility, because it is thought that phenolic or other reactive groups of the bitumen react very rapidly with free isocyanate groups of the polyurethane prepolymer, which likely leads to aggregations and therefore to instabilities of such a polyurethane-bitumen system.
Two or one-component polyurethane-coal tar combinations in solvents have been known for some time. However, due to the highly carcinogenic nature of coal tar, such combinations now lack any practical significance (cf. e.g. British Patent 1,323,884).
An object of the present invention is therefore to provide a polyurethane-modified bitumen composition having properties superior to those of conventional bitumen compositions.
Another object is to avoid the aforementioned disadvantages and to protect the environment by providing a solvent-free or low-solvent polyurethane-modified bitumen.
A further object is to provide a polyurethane-modified bitumen as a one-component composition which is stable in storage.
Yet another object is to provide a polyurethane-modified bitumen foam composition.